For use in a high-power, concentrated winding motor for HV or the like with a rotor in which large magnetic variations occur, rear earth magnets are fractured to reduce eddy-current loss.
Heretofore, one of this type of permanent magnet is disclosed in Patent Document 1 listed below. A permanent magnet of Patent Document 1 includes, as shown in FIG. 17, a cutting process of dividing a permanent magnet block 101 into separate permanent magnet pieces 102 by machining, a coating process of applying insulation treatment to each permanent magnet piece 102, and a joining magnetic variations occur of joining the separate permanent magnet pieces 102 having been subjected to the insulation treatment to each other with adhesive or the like into one body.
However, the machining performed in the cutting process of a manufacturing method of the permanent magnet in Patent Document 1 requires an expensive cutting tool provided with diamond chips to divide the permanent magnet block 101. The cutting tool is a wear-and-tear product that has to be replaced periodically. Therefore, such an expensive cutting tool with diamond chips is replaced every time it wears down, resulting in a problem with an increased cost. Further, the need to perform the coating process of applying the insulation treatment leads to an increased cost.
For the purpose of reducing the cost to divide the permanent magnet and lower the cost of insulation treatment, the present applicant proposed a manufacturing method including fracturing a permanent magnet according to Patent Document 2 listed below. As shown in FIG. 18, a permanent magnet block 201 is formed with fracturing notches 202 before being divided and then is fractured by a fracturing device 300. Since the permanent magnet block 201 is to be fractured, the block 201 can be divided by the fracturing device 300 using no cutting tool, forming separate permanent magnet pieces. The fractured block 201 not subjected to insulation treatment can provide almost the same effects as in the case where it is subjected to the insulation treatment. As a result, the cost of manufacturing the separate permanent magnet pieces and the cost of insulation treatment could be reduced.